Presently known assays for detection of hepatitis A antigen in biological liquids consist of the immune adherence hemagglutination assay described by Miller et al., Proc. Soc. Exp. Biol. Med., 149, 254-261 (1975) and the immune electron microscopic assay described by Feinstone et al., Science, 182, 1026-1028 (1973). Both of these methods are insufficiently sensitive to detect hepatitis A antigen in serum or plasma, and require a subjective evaluation to determine the end point.